Someone will probably be able to really clarify this... but in my OLD '84 wagoneer, there was a mess of vacuum tubing for the T-Case. the whole system for shifting between 2WD and 4WD was vacuum powered. It went like this: MAnifold vacuum supply to switch in truck, from switch to T-Case and then from T-Case to front axle. The tubing was actually connected to shift 'motors'; one on the T-case and one at the front axle differential. Throw in a few extra crossover tubes and a check valve or two, and that was how the old vacuum system worked. It all had to be in perfect condition to operate, sometimes if I had a leak it would shift the T-Case but not the front differential! Worse, If the shift motor on the T-Case wasn't adjusted just right, the T-Case may not be in 2WD completely causing damage to the internal parts....same with shifting to 4WD... that was such a pain in the ***, getting iy all dialed in though...
I guess I am surprised that there is any vacuum connection at such a late model Cherokee.... is just a vent tube? Like on an automatic transmission or some diff's?? The wiring may be for the back-up switch, usually 1 or 2 wires....
Hope this helps or triggers a more helpful response!